The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Powertrain systems employ internal combustion engines and non-combustion torque machines to generate tractive torque, execute engine autostop/autostart routines and effect vehicle braking. Non-combustion torque machines include electric motor/generator devices that couple to the driveline via a transmission element or via an engine crankshaft. Internal combustion engines are equipped with subsystems to improve engine efficiency and reduce fuel consumption including, e.g., cylinder deactivation systems, variable valve activation systems including variable cam phasing systems and variable valve lift systems, and engine autostop/autostart systems. Internal combustion engines can be controlled to spin in an unfueled condition during specific vehicle operating conditions such as decelerations, referred to as deceleration fuel-cutoff (dFCO). Energy is expended to spin an unfueled engine, referred to as engine pumping loss or engine drag torque.
Vehicle deceleration events provide opportunities to capture and store energy from vehicle momentum, such as during regenerative braking when a non-combustion torque machine effects vehicle braking through the driveline. It is appreciated that more energy of momentum is available for regenerative capturing during a deceleration event when engine drag torque is minimized. Engine drag torque can be minimized by employing one or more of the aforementioned subsystems that improve engine efficiency.
A transition in an operating state of an engine subsystem can induce torque vibration that can be transferred to a vehicle passenger compartment. Torque vibrations may be more noticeable at different vehicle and engine speeds due to the vibration occurring at a resonant frequency.